FIG. 4 is a cross-sectional view of a prior art multiple wavelength semiconductor light detector.
Reference numeral 1 designates incident light of wavelength .lambda.=1.3 microns. Reference numeral 2 designates incident light of wavelength .lambda.=1.55 microns. Reference numeral 8 designates an n-type InP substrate. Disposed on the n-type InP substrate 8 is an n-type InGaAsP layer 17 having an energy band gap corresponding to a wavelength of 1.55 microns and a p-type InGaAsP layer 16 having an energy band gap corresponding to a wavelength of 1.55 microns is disposed thereon. A p-type InP window layer 15 is disposed on the p-type InGaAsP layer 16. Disposed on part of the p-type InP window layer 15 is a p-type InGaAsP layer 14 having an energy band gap corresponding to a wavelength of 1.3 microns and an n-type InP window layer 12. A first n side electrode 18 is disposed on the n-type InP window layer 12. A p side electrode 19 disposed on the p-type InP window layer 15 is grounded. A second n side electrode 20 is disposed on the rear surface of the n-type InP substrate 8.
In this structure, n-type and p-type InGaAsP layers 17 and 16, p-type InP window layer 15, p-type and n-type InGaAsP layers 14 and 13, and n-type InP window layer 12 are successively epitaxially grown on the n-type InP substrate 8. Thereafter, the n-type InP window layer 12, n-type InGaAsP layer 13, and p-type InGaAsP layer 14 are etched to produce a mesa-type structure. Two n side electrodes 20 and 18 are respectively produced at the rear surface of the substrate 8 and the surface of the n-type InP window layer 12, respectively, and a p side electrode 19 is produced on the surface of the p-type InP window layer 15.
Light including components at a wavelength .lambda.=1.3 microns and a wavelength .lambda.=1.55 microns is incident on the surface. The p side electrode 19 is grounded and the first n side electrode 18 and the second n side electrode 20 are respectively biased at positive voltages. The light of wavelength .lambda.=1.3 microns transits the n-type InP window layer 12 and, thereafter, is absorbed by the InGaAsP layers 13 and 14, thereby generating charge carriers. In the pn junction between the InGaAsP layers 13 and 14, there is an electric field generated by a voltage applied from the outside. Therefore, the charge carriers generated by the irradiation of light are collected and generate an electromotive force between the first n side electrode 18 and the p side electrode 19. This electromotive force is extracted from the terminal OUT1 as an electrical output signal.
On the other hand, the light of wavelength .lambda.=1.55 microns transits the n side InP window layers 12 and 15 and InGaAsP layers 13 and 14 and is absorbed by the InGaAsp layers 16 and 17, thereby generating charge carriers. The charge carriers are output to the external terminal OUT2 as an electrical signal by the same process as described above. Herein, when the InGaAsP layers 13 and 14 are made sufficiently thick, the light of wavelength .lambda.=1.3 microns does not pass beyond the respective layers 13 and 14, and only the signal produced by the light of wavelength .lambda.=1.3 microns is output from the terminal OUTI and only the signal produced by the light of wavelength .lambda.=1.55 microns is output from the terminal OUT2. Therefore, this element functions as a multiple wavelength light detector.
In the prior art detector, however, the p side electrode 19 has to be connected to an internal layer in a multiple layer structure, the structure is thus complicated, and its production is difficult. Furthermore, matching of the light detector with other elements is more difficult than with a planar detector. In addition, since a crystalline surface is exposed, a surface leakage current flows, thereby reducing reliability.